I have a 2003 Mini Cooper S. Sometimes it makes this sound. It is more of rapid clicking but also a rattle. It used to do it every once in awhile and I didn't think much of it. It didn't make the sound for about the last 2 months. Then yesterday I wasn't paying attention and stalled it pulling out of the gas station, I cant even remember the last time I stalled it but when I started it back up it instantly started making this sound. Sometimes it goes away under acceleration but it always comes back and it is pretty loud when idling. Its been making the sound for a day now and I don't think I am going to drive it until I know whats up. Any help is appreciated. Thanks!

 

How many miles are on the car? And when you go under the hood where is the sound coming from? Give a google for supercharger rattle..I am hoping that isn't your issue because that's a pretty expensive fix. I am trying not to have you get the old google symptoms and then feel like you have them thing..but that's definitely a weird noise.

It doesn't really sound like timing chain rattle...but I am not 100% sure.

Try taking the video from under the hood

 

This sounds silly, but check the belt on the SC. Mine started to fray and it made a similar sound but it would sometimes go away

 

Its hard to tell in that video what sound I hear a tapping then a random clicking you need to make a better shot in daylight and go under the hood, could be a number of things from just this.

 

I had a rattle under the hood that I thought could be either the throw-out bearing or the supercharger sounding like a box of rocks. So I did a little investigating. I took off the airbox (bottom included) to get at my shifter linkages to lube them up as well. While looking around, to the left of the shifter linkages you will see a TON of wires all going to a plastic box looking thing. Well, that wire box is mounted to a bracket, which in turn is mounted to the block. There is a rather large grade 8 bolt that is used to bolt that bracket in. This bolt somehow worked it's way completely loose. I tightened the bolt down generously and now NO RATTLE!
It's crazy because I thought it was something a little more involved that just a bolt holding a bunch of wires in...